In a variety of engine-powered vehicles, monitoring devices have been employed to detect the presence of various undesirable engine operating conditions, such as overheating, low oil pressure, low fuel, electrical system faults and the like. Such systems have provided indicators, such as warning lights, for alerting an operator of these sensed conditions.
The importance of the various monitored engine conditions usually varies as to criticality. For example, an air filter for an engine or a filter for the hydraulic fluid may gradually clog during operation of the vehicle. The vehicle operator should be warned of such clogging, but generally there is no when the vehicle returns for normal servicing and maintenance. A low fuel condition requires more immediate attention from the operator A loss of engine oil pressure or a loss of hydraulic fluid represent conditions which require immediate operator attention to prevent damaging the vehicle
U.S. Pat. No. 4,184,146, which issued to Fratzke et al. on Jan. 15, 1980 and is assigned to the assignee herein, recognizes and partially addresses the above problems. Fratzke al. provides a system for warning a vehicle operator of an undesirable operating condition of one or more of a plurality of monitored operating parameters of an engine-powered vehicle. Three degrees of warning are given, depending upon the criticality of the monitored parameter. Individually energizable low-intensity warning indicators are provided for each of the monitored parameters, and a multiplexing circuit is provided for staggered pulsing of the indicators. The existence of any critical fault will cause an intermittent operation of a more intense warning device, while the existence of a highly critical fault results in an additional intermittent warning of a still greater degree of intensity.
However, if an operator ignores the warnings and continues to operate the vehicle, it is possible for the vehicle to be severely damaged. U.S. Pat. No. 5,070,832 issued to Hapka et al. is directed toward derating engine power in response to detecting certain faults relating to engine fluid levels. Hapka includes a second derate schedule for more severe fault conditions. According to this second schedule, the maximum engine speed is gradually reduced over a certain time period and to a certain percentage of the normal maximum engine rpm.
In vehicles having a hydrostatic transmission, other faults can be present that will go undetected by an engine controller such as the one disclosed in Hapka. Those other faults can detrimentally affect vehicle performance and may prevent the vehicle from being operated. For example, in a vehicle propelled using tracks, if the transmission for one of the tracks fails, then operating the other track will not allow the vehicle to move forward. Similarly, in transmissions that have a plurality of gear ratios a transmission fault could effect vehicle performance. In either of these cases, the engine may operate normally, but continued operation of the vehicle could damage the transmission or other portions of the vehicle.
It would be preferable to have a transmission monitoring and control system that limits maximum vehicle speed and vehicle direction in response to a sensed transmission fault.
Some transmission faults may not create an imminent danger of damage to the vehicle. Other faults may have a greater tendency to damage the vehicle at one level as opposed to other levels.
It would be preferable to have a transmission monitoring and control system that could classify sensed faults according to the likelihood that the fault would damage the vehicle under continued operation. Such system would preferably include a graduated reduction in maximum vehicle speed corresponding to the classification of the sensed fault.
The present invention is directed towards overcoming one or more of the problems as set forth above.